Field of the Invention
The present invention relates to an image pickup apparatus such as a surveillance camera e.g. a network camera equipped with an illumination unit, and an image monitoring system.
Description of the Related Art
Some network surveillance cameras incorporate an illumination unit between a dome-shaped cover, which protects an image pickup unit, and the image pickup unit so as to enable shooting in dark places. In the surveillance cameras, a light-shielding member is provided between the image pickup unit and the illumination unit so as to prevent illumination light, which is emitted from the illumination unit toward a subject, from being reflected on the dome-shaped cover or the like, entering a lens of the image pickup unit, and appearing in a captured image (Japanese Laid-Open Patent Publication (Kokai) No. 2005-136800).
On the other hand, particularly in a surveillance camera for which a sealed structure is adopted, condensation and frost occur on inner and outer surfaces of a dome-shaped cover due to insufficient circulation of air in the surveillance camera or a temperature difference between an inside and outside of the surveillance camera in a low-temperature environment and the like. This leads to degradation in sharpness of a captured image. For this reason, there has been proposed a technique according to which condensation and frost are prevented from occurring on the inner and outer surfaces of the dome-shaped cover by causing air to circulate in the surveillance camera through natural convection using a permeable film or a dehumidification element provided inside the surveillance camera, or by forcing air in the surveillance camera to circulate using a fan or the like (see Japanese Laid-Open Patent Publication (Kokai) No. 2009-135723).
According to Japanese Laid-Open Patent Publication (Kokai) No. 2005-136800 above, however, an annular light-shielding member is placed in a state of being brought into close contact with an inner wall of the dome-shaped cover. Therefore, when air inside the surveillance camera is circulated using the permeable film or the dehumidification element or using the fan, air resists being circulated between a space on a front side of the lens unit and on an inner peripheral side of the light-shielding member and a space inside the dome-shaped cover and on an outer peripheral side of the light-shielding member. Thus, in the surveillance camera equipped with the illumination unit, it is difficult to prevent condensation and frost from occurring on the inner and outer surfaces of the dome-shaped cover.